Elenco's Night 'n Day Mechanical Globe uses a system of translucent, exposed gears to rotate an internally illuminated globe that displays the seasonally adjusted, real-time night/day terminator as it spins.
The reviews indicate some build quality problems, with customers having to return their units to get a complete one, so caveat emptor, but it looks like if you're willing to put up with that hassle you will get a fully functional (and awfully cool) STEM gadget — at $173, you'd think they could sort this out (and perhaps they have, as the complaints are rather old), but apart from the QA issues, I love everything about this (I'm such a sucker for exposed mechanisms!).
The Night'n Day Real Solar Time Rotating Globe is a clock and calendar that shows the time of day and date for any location on earth. It also demonstrates which parts of the earth are in day or night. As the globe turns, you can see where people on earth are experiencing sunrise, sunset and twilight times. Features: 11" (28cm) globe. Assembly and easy set-up required, AC adaptor included.
(via Red Ferret)